Cathode ray tube (CRT) displays are commonly used in display devices such as televisions and desk-top computer screens. CRT displays operate as a result of a scanning electron beam from an electron gun striking phosphors resident on a distant screen. The electrons increase the energy level of the phosphors. When the phosphors return to their original energy level, they release photons which are transmitted through the display screen (normally glass) forming a visual image to a person looking at the screen. A colored CRT display utilizes an array of display pixels wherein each individual display pixel is comprised of a trio of color generating phosphors (that is, each pixel is split into three colored parts, which alone or in combination create colors when activated). Color images are created by exciting the appropriate colored phosphors.
Flat panel displays are becoming more popular in today's society. These displays are being used more frequently, particularly to display the information of computer systems and other devices. Typically, flat panel displays are lighter and utilize less power than conventional CRT display devices.
There are different types of flat panel displays. One type of flat panel display is known as a cold cathode field emission display (FED). Cold cathode FED's are similar to CRT displays in that they use electrons to illuminate a cathodoluminescent screen. The electron gun is replaced with numerous (at least one per display pixel) emitter sites. When activated by a high voltage, the emitter sites release electrons which strike the display screen's phosphor coating. As in CRT displays, the phosphor releases photons which are transmitted through the display screen (normally glass) forming a visual image to a person looking at the screen. A colored FED display utilizes an array of display pixels wherein each individual display pixel is comprised of a trio of color generating phosphors (that is, each pixel is split into three colored parts which alone, or in combination create colors when activated). Color images are created by exciting the appropriate colored phosphors.
In order to obtain proper operation of the flat panel display, it is extremely important for a FED of the cold cathode type to maintain an evacuated cavity between the emitter sites (acting as a cathode) and the display screen (acting as a corresponding anode). The typical cold cathode FED is evacuated to a pressure of 10.sup.-6 Torr or less. This reduced atmospheric pressure is required to allow electron emission. In addition, since there is a high voltage differential between the screen and the emitter sites, the reduced pressure is also required to prevent an electrical breakdown.
The reduced atmospheric pressure presents several problems. Firstly, the spacing between the emitter sites and the screen must be uniform and narrow to retain high resolution images and requisite thinness of the FED. Uneven spacing is likely due to the high pressure differential existing between the external atmosphere and the pressure within the evacuated cavity of the FED. This spacing problem worsens as the display screen gets larger. In addition, the reduced pressure places a tremendous atmospheric load on the FED's screen. This load may cause the screen to warp. Therefore, cold cathode FEDs require additional structure (such as spacers or thicker components) to prevent these problems.
Another popular flat panel display is a plasma based or gas discharged display. Plasma based flat panel displays generally utilize an enclosed gas or gas mixture in a partially evacuated cavity. Crossed conductors (acting as opposed electrodes) are placed within the cavity to break down the gas into a plasma of electrons and ions causing a visible glow. In a monochrome monitor, a light emitting gas, such as neon, or light generating phosphors are used to generate visual images. Generally, each display pixel has at least one corresponding crossing point.
A colored plasma display utilizes an array of display pixels wherein each individual display pixel is comprised of a trio of color generating phosphors (that is, each pixel is split into three colored parts, which alone or in combination create colors when activated). Accordingly, the colored display pixel would have three crossing points corresponding to each color generating phosphor. Color images are created by exciting the appropriate color generating phosphors.
In order to obtain proper operation of the gas discharged flat panel display, it is extremely important that a partial vacuum be maintained within the cavity containing the crossed conductors and the gas. The partial vacuum is required to maintain the minimum firing voltage of the gas disposed within the cavity (according to Paschen's Law, the minimum firing voltage of a gas is a product of the gas pressure and the distance between the electrical conductors).
As with cold cathode FEDs, the reduced pressure inside the gas discharge display presents several problems. For example, reduced pressure places a large atmospheric load (approximately 15 pounds per square inch) on the screen. Special manufacturing techniques are required to alleviate the implosive forces exerted on the display. Secondly, rare gases must be used in order to achieve the requisite breakdown into plasma presenting additional manufacturing difficulties. These troubles have made it difficult to use high resolution plasma based displays in computer workstations.
Attempts have been made to correct the shortcomings of the flat panel display. For example, U.S. Pat. No. 5,654,727 (Lepselter) discloses a gas discharge flat panel display operable at substantially atmospheric pressure. The disclosed apparatus utilizes a first set of conductors spaced apart at a precise distance from a second set of conductors in a crossed pattern. The cross points of the conductors are used to energize a gas held at a precise pressure in order to give off a light emissive discharge. The disclosed apparatus utilizes an additional layer of substrate, which is then sacrificially discarded, to maintain the required spacing between the crossed conductors.
Although advances have been made, prior art flat panel displays often require additional, or intermediate, layers of substrate or additional structures to maintain precise spacing or pressure. In addition, flat panel displays often require special gases, high vacuums or high power. Accordingly, a low powered flat panel display containing a confined gas which is nearer to atmospheric pressure and has a simplified manufacturing process is still needed.